(1) Field of the Invention
This invention relates generally to Liquid Crystal Displays (LCD) and relates more particularly to an interlaced technology to connect an LCD display controller device to a LCD display.
(2) Description of the Prior Art
Liquid Crystal Displays (LCDs) are used everywhere, for example TVs, laptop computers, CD players, digital clocks, watches, and many other electronic devices. They are common because they are thin, flat, having a high resolution with low voltage operation and low power consumption.
In order to build LCDs liquid crystals are placed between two sheets of glass, which are grooved to control the alignment of the molecules, i.e. the way they arrange themselves. The molecules follow the alignment of the grooves: if the grooves are parallel to each other so are the liquid crystal molecules. If the grooves on one sheet of glass are aligned north to south and the grooves on the other east to west, the molecules twist in between the sheets of glass. Light goes through the molecules and follows their alignment twisting 90 degrees as well. A voltage makes the molecules arrange themselves vertically which causes the light go through them untwisted.
On the two sheets of glass there are polarizing filters which prevent all other light waves expect the ones that come parallel to the filters. The filters are placed so that one is at 90 degrees to the other. This would block the light because to let the light go through the filters should be parallel. But as the liquid crystals are twisted the light passes through the second filter by following the twist of the molecules. Because liquid crystal molecules rearrange themselves vertically when a voltage is applied it is possible to block the light when wanted and prevent the light emerging from the other end. Thus there are two states: 1) no voltage, which means light passing through and 2) applied voltage, which prevents the light coming out of the other end.
The orientation of the alignment layers varies between 90 and 270 degrees. By the degree of the twist nematic LCDs can be divided into two groups: LCDs with 90 degrees twist are called twisted nematic (TN) and with 270 degrees super twisted nematic (STN) displays.
Due to the relative slow response of the liquid crystal (LC) material itself to changes in addressing voltages a phenomenon called “smearing” appeared in the display of fast moving objects. In order to enable screens to display video images, new LC materials were developed with lower viscosity. If the viscosity of LC material is lowered so as to realize fast response, the root-mean-square (rms) response of liquid crystal is disabled but the frame response (response to the driving voltage waveform itself) is enabled. Consequently, if the liquid crystal is driven by the conventional line-by-line selection addressing, in which the applied voltage is concentrated in one part of one frame period, the transmission of off display pixel parts increases and the transmission of on display pixels reduces. As a result, the contrast of displayed images lowers, so that satisfactory display characteristics cannot be obtained.
Multiple line addressing (MLA) has been recently introduced as a driving method, which can suppress the above-mentioned frame response phenomenon. The feature of MLA is that several scanning lines can be selected simultaneously, and the selection pulse interval can be shortened without the selection pulse width. This implies that the selection pulse can be dispersed over one frame period. As a result, the frame response phenomenon can be suppressed, and high contrast can be obtained.
FIG. 1 prior art shows a conventional scheme to interconnect a display controller device 1 with a MLA STN display 2. It is obvious to those skilled in art that FIG. 1 prior art shows an example only. The number of sub-groups is in reality much higher compared to the number of sub-groups shown in FIG. 1 prior art. In this scheme the upper half 3 of the display has its MLA common sub-groups driven from the left of the display controller device 1. The lower half of the display has its MLA common sub-group driven from the right of the display controller device 1. In this example an MLA scheme using three common lines 5 to make up a sub-group is shown. The vertical “segment” columns are connected to the middle of the display controller device 1 by segment lines 6.
It should be understood that the common sub-groups are not always all driven from the topside of the display controller device. Sometimes they are driven from the left-hand end and right-hand end of the device. Sometimes they are driven from the bottom side of the device
It is a challenge for a designer of such display systems to minimize the resistance of the common lines and to avoid a marked difference in routing distance between the lowermost common sub-group display lines in the upper half of the display and the uppermost common sub-group display lines in the lower half of the display. A difference in routing can produce a difference in contrast, which is undesirable between adjacent display lines.
There are patents and patent applications publications known dealing with the challenges of said display systems.
U.S. Pat. No. (6,346,774 to Tamai et al.) describes a method of driving a passive matrix of a LCD. Driving is effected by MLA under a condition of L.noteq.M or (M/L.multidot. (L+D)). noteq.N where M represents the total number of row electrodes, L represents the number of simultaneously selected row electrodes, D represents the number of dummy row electrodes and N represents the maximum magnifying power of a column voltage wherein driving is performed at a driving bias ratio which is deviated toward the minimum bias ratio with respect to the optimum bias ratio.
U.S. Patent Application Publication (2003/0193491 to Lawrence et al.) discloses a display device having a number of pixels to display an image. A first set of electrodes and a second set of electrodes are provided. To display an image in accordance with image data, the first and second sets of electrodes are addressed with a first set of drive signals and a second set of drive signals respectively in order to drive the pixels of the display device. The first set of drive signals is predefined. The image data is compressed. The second set of drive signals is obtained from the compressed image data.
U.S. Patent Application Publication (2002/0158832 to Park et al.) describes a driver for driving an STN LCD. A preferred embodiment comprises a 3-line output display data for storing display data, an XOR block for finding mismatches between each 3-line output set of the stored display and orthogonal function signals, a decoder block for calculating mismatch numbers, a level shifter block for shifting the data level of the mismatch numbers to another level, and a voltage selector block for selecting a voltage level from 2 levels of voltage. Because data latches and output latches are not necessary, the driver of the present invention achieves significant reduction in the circuit components and chip size without compromising the display quality.